There is an increasing demand for integrated circuits to operate at millimeter wave (mm Wave) frequencies. Silicon germanium (SiGe) bipolar complementary metal oxide semiconductor (BiCMOS) technology is a natural choice for such an application due to its high performance bipolar transistor integrated with high quality passives and CMOS devices. SiGe heterojunction bipolar transistors (HBTs) have shown steady improvement with a recent report of 300/350 Ghz fT/fmax, which enables various mm Wave applications. However, for a technology to be mm Wave capable one must look beyond the high speed transistors and evaluate the passive components such as Schottky barrier diodes (SBDs), PIN diodes, and varactor diodes.
An SBD with a cutoff frequency (Fc) above a terahertz enables designs such as mixers, high speed sample and hold circuits at mm Wave frequencies. In other applications, the SBD is used as a rectifier in power detectors for power amplification circuits. Low leakages in the off state translate to superior hold times in sample and hold circuits. For a power detector, low leakage is necessary due to noise constraints.
Additionally, high frequency applications, such as millimeter wave devices (f>30 GHz), require multifunction circuits with different types of devices for optimum operation. For example, in advanced microwave devices, transmitter circuits of communication and radar systems use heterojunction bipolar transistors (HBTs). But, in this same device, receiver circuits comprise field effect transistors (FETs), such as high electron mobility transistors (HEMTs), to minimize the noise figure and therefore improve the receiver sensitivity. The performance of such multifunction circuit devices can be reduced if all of the subsystem functions can be accomplished with the use of a common device process technique to integrate all of the relevant advanced devices onto the same substrate.
Prior generation SBDs have utilized implanted subcollectors and shallow and deep buried subcollectors. An SBD with an implanted subcollector, while exhibiting good leakage characteristics (i.e., low leakage), suffers from a low Fc. Further, an SBD with a shallow subcollector suffers from both a low Fc, due in part to a high capacitance, and a high amount of leakage. Additionally, an SBD with a deep subcollector exhibits a low leakage and a high Fc. However, a deep subcollector detrimentally impacts the performance of the high speed transistors, e.g., HBTs. Thus, manufacturing an SBD and a transistor on the same wafer using a single subcollector for both the SBD and the transistors may prevent optimization of both devices.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.